# Question Video: Identifying a Pattern Produced by Light Diffracted through Nearby Gaps Physics • 9th Grade

A light source emits light that passes through two narrow slits and then falls onto a screen, as shown in the diagram. Which of the four patterns on the screens (A), (B), (C), and (D) most correctly shows the pattern that would be produced on the screen by the light diffracted through the slits?

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### Video Transcript

A light source emits light that passes through two narrow slits and then falls onto a screen, as shown in the diagram. Which of the four patterns on the screens (A), (B), (C), and (D) most correctly shows the pattern that would be produced on the screen by the light diffracted through the slits?

To begin, let’s clear some space on screen and recall some basic information about diffraction patterns produced by light passing through two narrow slits.

First, we know that due to its wavelike nature, as light passes through the slits, it interferes with itself constructively and destructively. We can see this by placing a screen next to the slits and noticing that the interference of the light waves results in areas of alternating brightness and darkness on the screen. This is known as a diffraction pattern, as the light was diffracted as it passed through and bent around the two slits.

For light passing through two identical slits, like in this question, the diffraction pattern is symmetric. We also expect that the brightest area on the screen is in the center, directly between the two slits.

With all this in mind, let’s look over the four patterns given in the diagram. Pattern (A) appears to obey the conditions we just mentioned. The pattern of alternating brightness and darkness is symmetric and brightest in the very center. This seems to be a good option then.

Next, we see that pattern (B) is brightest in the center, but there’s no real pattern here. We expect to see alternating bright and dark spots, not just one big bright spot, so this isn’t the best option.

Moving on, pattern (C) is symmetrical, and we do see different areas of alternating brightness. But the very center of the screen here is dark. We’ve already established that this should be the brightest spot, so (C) isn’t a good option either.

Finally, pattern (D) is all over the place. There are alternating bright and dark spots, but they’re not symmetrical. And the very center of the screen has a dark spot, so we know that this isn’t right either.

Thus, we’ve seen that pattern (A) is, in fact, the best option, as it shows the properties we would expect of a diffraction pattern produced by light passing through the two slits.